HYDROGEN IONS, TITRATION AND THE BUFFER 

 INDEX OF BACTERIOLOGICAL MEDIA 



J. HOWARD BROWN 



From the Department of Animal Pathology of The Rockefeller Institute for Medical 

 Research, Princeton, New Jersey 



Received for publication April 19, 1921 



Of recent years bacteriologists have become familiar with the 

 determination of hydrogen ion concentration as applied to the 

 problems of bacteriology. In many if not most laboratories 

 media are properly adjusted to certain hydrogen ion concentra- 

 tions, and the changes in reaction produced by the growth of 

 organisms in these media are likewise determined in terms of 

 hydrogen ion concentration. It has been repeatedly pointed out 

 that media of the same titratable acidity or alkalinity may differ 

 widely in their actual or true acidity or alkalinity. It is known 

 that an acid-forming organism growing well in the presence of an 

 excess of fermentable sugar in different bouillons may arrive at 

 approximately the same final hydrogen ion concentration in each 

 medium, whereas the titratable acidities of the cultures may 

 differ widely. Who of us has not been confronted repeatedly 

 by such questions as — Why do you titrate your cultures? Is not 

 the true acidity found by the determination of hydrogen ion 

 concentration and is it not much simpler? Why bother with 

 titration? To which the answer is — Yes, but titration and 

 hydrogen ion determination tell entirely different stories: they 

 are not simply two methods, one more accurate than the other, 

 of determining the same thing. 



The committee on the Descriptive Chart of the Society of 

 American Bacteriologists (1919) has published the statement 

 that ''the titration method (is) entirely illogical for adjusting 

 the reaction of media or for determining the amount of acid 

 produced by an organism." To both parts of this statement 



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JOURNAL OF BACTERIOLOGY, VOL. VI, NO. 6 



